> If you have hundreds of jobs like this you need a proper queue and neither cronie nor systemd is the right tool
Eh sometimes, but you can get pretty far with one of two approaches:
1. Careful use of Requires= and Wants= to group your scripts into chains of jobs, which achieves fixed parallel (though at 100s of jobs, I hope you're generating those unit files with a tool like Puppet or https://github.com/karlicoss/dron or something and not doing this by hand).
2. Even better, just use a lockfile. `ExecStart="flock -F $TMPDIR/mylock <command>"` is pretty hard to beat. Use -F so as not to confuse KillMode and resource accounting and you're golden. Just don't use flock(1) timeouts; let systemd handle that. Heck, if you have that many cron jobs, you should be doing this even if you don't use systemd; otherwise job latency changes can cause reboot-style thundering herds out of the blue.
1. This is spread across 500 files, maintainability goes out the window
2. If this for some reason fails, misconfiguration or unexpected shutdown, you could have a failure that's hard to track or debug
These are fine with a few services chained together, but this requires a shallow depth of dendencies. To have these theoretical hundreds of jobs chained together like this isn't practical or safe.
Eh sometimes, but you can get pretty far with one of two approaches:
1. Careful use of Requires= and Wants= to group your scripts into chains of jobs, which achieves fixed parallel (though at 100s of jobs, I hope you're generating those unit files with a tool like Puppet or https://github.com/karlicoss/dron or something and not doing this by hand).
2. Even better, just use a lockfile. `ExecStart="flock -F $TMPDIR/mylock <command>"` is pretty hard to beat. Use -F so as not to confuse KillMode and resource accounting and you're golden. Just don't use flock(1) timeouts; let systemd handle that. Heck, if you have that many cron jobs, you should be doing this even if you don't use systemd; otherwise job latency changes can cause reboot-style thundering herds out of the blue.
If you need semaphore behavior and still don't want a real job queue, waitlock (https://github.com/bigattichouse/waitlock) and many other CLIs have you covered.